Method
1. Marinate chicken pieces with ground masala paste, chopped mint leaves and 1/4 tsp turmeric powder.
2. Mix 2 cups of coconut milk with 4 cups of water.
3. Soak basmati rice in coconut milk and water mixture for half an hour.
4. Heat oil in a heavy bottom pan with lid, when oil is hot add bay leaves and onions. Saute onions until they are slightly browned.
5. Now add the marinated chicken along with masala & mint leaves to the sauted onions and fry until the chicken turns pale in color.
6. Next add the chopped tomatoes, curd, red chilli powder and rest of turmeric powder to the pan.
7. Saute well until tomatoes are cooked, add few tbsps of water to the pan, stir well everything.
8. When light gravy is formed, reduce heat, cover pan with tight lid and leave chicken to cook in gravy for 10 mins.
9. After 10 mins add coconut milk & water mixture from soaked basmati rice and required salt for making biryani to the gravy.
10. Turn the heat to high and bring the biryani gravy to boil.
11. When gravy starts boiling add soaked basmati rice to the pan and stir well.
12. When 1/2 of water is absorbed by the rice, reduce heat to low, cover pan with tight lid and cook biryani rice until tender.
13. Finally garnish chettinad chicken biryani with coriander leaves and fried cashew nuts.
Serve hot with onion raita, plain salna and boiled egg.

Chef's tips
My grandma and mom used to prepare biryani with regular raw rice( ponni rice) or with seeraga samba rice. They brought flavors to biryani with hand ground masala, coconut milk and with country chicken but now it had become custom to cook biryani with basmati rice.

You can omit coconut milk and place it with water but coconut milk makes big difference in preparing chettinad style biryani.

While grinding masala paste some prefer to add fennel seeds for more flavor. If you prefer to do so add about 1 tbsp roasted fennel seeds( Sombu).